Certain techniques for the 3D printing of polymers, such as digital manufacturing systems, require the use of a sacrificial polymer to “support” the polymer of the object to be printed. This technique and the characteristics of this sacrificial polymer are described in WO 2010/045 147. According to said document, the main characteristics of this sacrificial polymer must be:                solubility in aqueous medium (which is usually alkaline);        a creep relaxation transition temperature (which is directly linked to the glass transition temperature Tg, according to the measuring protocol described in patent U.S. Pat. No. 5,866,058) of the order of that of the polymer to be printed (or of one of the fractions of the polymer to be printed). For example, for the printing of ABS, the Tg of the sacrificial polymer must be at least 120° C.;        a capacity to be compounded with additives allowing an improvement in the mechanical properties.        
The support material described in WO 2010/045 147 contains a copolymer and a polymeric impact modifier. According to one embodiment, said copolymer comprises monomer units bearing a carboxyl group and monomer units comprising a phenyl group. According to another embodiment, the support is formed from a first copolymer and a second copolymer. Said first copolymer comprises monomer units bearing a carboxyl group, monomer units comprising a phenyl group and monomer units comprising carboxylate ester groups. Said second copolymer comprises a plurality of epoxy-terminated carboxylate ester groups. Examples 1-15 describe the use as support material of a mixture of copolymer and of impact modifier, said copolymer being based on butyl acrylate, styrene and methacrylic acid. Partial anhydrification of the acid functions allows it to achieve Tg values of the order of 120° C. (measured by DSC) and thus to be able to print polymers such as ABS. The system used in said patent is derived from the compounding of the copolymer with an impact additive of the type such as Elvaloy® (DuPont) and/or Lotader® (Arkema). During the preliminary compounding step, the impact modifier reacts, via the epoxy functions, with the acid functions of said copolymer.
The Applicant has now found that it is possible to prepare a block copolymer acting solely as support material, said block copolymer having the properties required to fulfil this function (namely solubility in aqueous medium and a high glass transition temperature Tg of the major phase, preferably above 120° C.) without it being necessary to mix it beforehand with an additive.